1. Field of the Invention
This invention relates to percussion tools, and more particularly to an improved manner of securing the tool shaft or moil and to an improved cushioned moil stop.
2. Description of the Prior Art
Percussion tools of the type generally similar to the improved percussion tool of the the present invention basically comprise a casing or housing from which a moil or tool shaft projects. A projecting knob or collar on the moil retains the moil within the casing. A reciprocating hammer within the casing drives the moil so that it reciprocates forcefully during use, causing the moil to break up or penetrate whatever work piece to which it is applied. An example of this type of percussion tool is disclosed by my U.S. Pat. No. 3,739,863, granted June 19, 1973. Another example is the common handheld jackhammer.
As disclosed in my aforementioned U.S. Pat. No. 3,739,863, the means driving the moil may be a gas spring driven piston or hammer which repeatedly strikes the top of the moil, causing the moil to be propelled forcefully downwardly. Between the blows of the piston or hammer, the weight of the percussion tool and the rebound of the moil from the work piece help to return the moil to its starting position.
Thus, it is seen that during the use the moil will move back and forth through a fairly constant range of travel. However, in certain instances, such as when the material being worked on suddenly breaks or moves away, or when the impact tool is inadvertently actuated while the moil is not in contact with the workpiece, the moil will exceed a predetermined range of travel and collide with an internal structure of the percussion tool. As can be appreciated, due to the substantial forces involved, repeated collisions between the knob or collar on the moil and the internal structure of the impact tool often result in such damage that the impact tool is rendered inoperable and in need of costly repair.
It is known to provide a moil with a recessed portion which defines a shoulder that collides with a transverse stop pin which the moil exceeds a predetermined range of travel during use. It can be appreciated that the resulting jarring metal-to-metal impact between the moil and the stop pin often shears the stop pin or results in a jammed moil due to mushrooming of the moil in the region of its impact with the stop pin.
Cushioned moil stops have also been deviced, such as that disclosed in U.S. Pat. No. 1,774,905 granted Sept. 2, 1930 to Smrdel, which include an elastic buffer. In the Smrdel moil stop, the elastic buffer is enclosed between the elongated nosecap of the impact tool and a split, flanged bushing which surrounds the moil. The upper end of the moil includes an outwardly projecting collar, of greater diameter than the shaft of the moil, which strikes the flange on the split bushing when the moil moves past a predetermined position, thereby compressing the buffer and stopping the moil.
The Smrdel moil stop suffers from a drawback in that its cylindrical lower casing, which encloses the elastic buffer, does not allow unlimited outward flow of the elastic buffer when it is compressed. This may result in less than optimum cushioning, if an insufficient flow space is provided for the compressed buffer. Such a construction may also result in rapid wear and early failure of the buffer since, when it is compressed, it may be forced inwardly against the moving flanged bushing which surrounds the moil. In addition, the long tubular form of buffer results in the possibility that the buffer may buckle when compressed, which would also force certain portions of it against the moving flanged bushing, again resulting in the possibility of rapid wear and early failure of the buffer.
The collared moil utilized in the Smrdel device also presents problems. It is apparent that, if the moil also has an enlarged or angularly disposed work tip such as that disclosed in U.S. Pat. No. 1,470,622 granted Oct. 16, 1923 to Jimmerson, in order to permit insertion or removal of such a moil through the nosecap, the aperture for the moil in the nosecap may have to be sized larger than the main shaft of the moil in order to permit passage of the collar on the moil. As can be appreciated, the extra space between the moil and the nosecap resulting from such an enlarged aperture leaves the lower portion of the flanged bushing, and thus the moil, with support which may be less than adequate and thus may subject it to unwanted sidewise displacement. In addition, the enlarged aperture may lead to early failure of the buffer if it is dragged down into said aperture by the flanged bushing which surrounds the moil, when the bushing is displaced downwardly by the moil. Similarly, such undesired entry of the buffer into said enlarged aperture may also occur when the buffer is subjected to compression by the flanged bushing, thereby squeezing it into said aperture. Finally, with such a construction, both the flanged bushing and the elastic buffer apparently have to be of a split construction in order to permit insertion or removal of the moil. Naturally, such split construction results in increased cost and makes assembly and disassembly of the device a cumbersome task.
In order to prevent these problems, it is possible that the enlarged or angularly disposed work tip be threadedly connected to the moil, but of course such a solution leads to its own problems in that the forces involved during operation of the impact tool may damage the threads or cause the work tip to be jammed onto the moil, thereby making it quite difficult to remove, as well as being expensive.
A further disadvantage of the Smrdel impact tool is that its nose bushing may be subject to early failure because of the wear caused by the relative movement of the longitudinally vibrating moil within it. Applicant theorizes that this rapid wear is due to the fact that, when the moil is displaced sideways into contact with the bushing, there is only a single line of contact between the cylindrical shaft on the moil and the larger, cylindrical bushing which surrounds it.
Another disadvantage of the prior art devices is that their nosecaps are usually secured to the main body of the impact tool by costly and complex spring arrangements, or by costly and damage prone threads or transverse bolts. Such constructions have the further disadvantage in that they may be cumbersome and awkward to assemble or disassemble with it is necessary to remove the nosecap in order to insert, remove or index the moil. In addition, such constructions may increase the overall diameter of the casing of the impact tool beyond what is strictly necessary.